Manufacture of semiconductor integrated circuits and other micro-scale devices typically requires formation of multiple metal layers on a wafer or other substrate. By electroplating metals layers in combination with other steps, patterned metal layers forming the micro-scale devices are created.
Electroplating is performed in an electroplating processor with the device side of the wafer in a bath of liquid electrolyte, and with electrical contacts on a contact ring touching a conductive layer on the wafer surface. Electrical current is passed through the electrolyte and the conductive layer. Metal ions in the electrolyte plate out onto the wafer, creating a metal layer on the wafer.
Electroplating processors typically have consumable anodes, which are beneficial for bath stability and cost of ownership. For example, it is common to use copper consumable anodes when plating copper. The copper ions taken out of the plating bath are replenished by the copper coming off of the anodes, thus maintaining the metal concentration in the plating bath. This is a very cost effective way to maintain the metal ions in the bath compared to replacing the electrolyte bath in a bleed and feed scheme. However, using consumable anodes requires a relatively complex and costly design to allow the consumable anodes to be replaced. Even more complexity is added when consumable anodes are combined with a membrane (for example a cation membrane) to avoid degrading the electrolyte, or oxidizing the consumable anodes during idle state operation, and for other reasons.
Such systems require many mechanical parts for seals and membrane supports. Electroplating processors using inert anodes have been proposed as an alternative to using a consumable anode. An inert anode reactor holds promise to reduce chamber complexity, cost, and maintenance. However, use of inert anodes has led to other disadvantages, especially related to maintaining the metal ion concentration in a cost effective manner compared to consumable anodes and the generation of gas at the inert anode which can cause defects on the workpiece. Accordingly, engineering challenges remain to providing an inert anode electroplating processor.